1. Field of Invention
The present invention relates to a capacitance sensing switch, and more particularly to a capacitance sensing switch used on a glass-ceramic cooktop.
2. Description of Related Art
A glass-ceramic cooktop not only has a beautiful appearance but also is easily to clean the cooking surface. Therefore, the glass-ceramic cooktop has become a standard kitchen appliance for the purpose of cooking food.
FIG. 1 illustrates a schematic diagram of a traditional glass-ceramic cooktop. The traditional glass-ceramic cooktop 100 includes a glass plate 101, five burners 102 on the top and installed into the glass plate 101, and a control region 103 formed in the glass plate 101. A plurality of capacitance sensing switch keys is formed in the control region 103 to control the five burners 102 respectively. A capacitance sensing switch key includes a capacitor. When a conductor, such as a finger, touches the capacitance sensing switch key, some charge stored in the capacitor of the capacitance sensing switch key is moved to the conductor, which results in the change of the capacitance of the capacitor. A micro-controller detects the capacitance change to trigger a corresponding operation.
However, the performance of a capacitance sensing switch key is easily affected by environmental factors. For example, when burning soup in a burner, the spilled soup can touch a capacitance sensing switch key to trigger an unwanted operation to cause a dangerous situation. On the other hand, because the glass plate 101 is an insulation material, these capacitance sensing switch keys 102 built in the glass plate 101 are insulated to each other. Therefore, when a user touches one of the capacitance sensing switch keys, only the charges stored in the touched capacitance sensing switch key are redistributed. The charges stored in other capacitance sensing switch keys are kept. Therefore, only the corresponding operation controlled by the touched capacitance sensing switch key is triggered. However, if the capacitance sensing switch keys are built in a conductor plate, the capacitance sensing switch keys are conducted to each other. Therefore, when a user touches one of the capacitance sensing switch keys, the charges stored in all capacitance sensing switch keys are redistributed. The micro-controller can not determine which one of the capacitance sensing switch keys is touched, which will cause a mistake operation. That is, a glass plate has to be adopted to form a cooktop when a user wants to use the capacitance sensing switch keys to control the burners, which is not convenient for a kitchen designer.